Capacitive sensors operate by detecting changes in the capacitance formed between a transmission electrode and a sense electrode. A sensing circuit can recognize an object and determine the location, pressure, direction, speed and acceleration of the object as it is approaches and/or moves across the touch surface.
Electronic devices with touch sensing surfaces may utilize various capacitive sensing devices to allow a user to make selections and move objects by moving their finger (or stylus) relative to a capacitive sensing element. The capacitive sensing device may utilize mutual capacitive sensing or self-capacitance sensing. Mutual capacitance touch sensors not only have the ability to detect touch events on the sensing surface, but also have the ability to detect proximity events, in which an object is not touching the sensing surface, but is in close proximity to the sensing surface. The mutual capacitive touch sensor operates by measuring the capacitance of the capacitive sense element, and looking for a change in capacitance indicating a touch or presence of a conductive object. When the conductive object (e.g., a finger, hand, foot, or other object) comes into contact or close proximity with a capacitive sense element, the capacitance changes and the conductive object is detected. An electrical circuit may be utilized to measure the change in capacitance of the capacitive touch sense element, and the electrical circuit may convert the measured capacitance of the capacitive sense element into a digital value.
Conventional devices that are capable of both proximity and touch sensing must generally rely on additional pressure sensors and/or a resistance film sensor to detect when a firm pressure is applied to the sensing surface, which may increase the overall cost of the device.